Indications for very high metallicity and absence of methane for the eccentric exo-Saturn WASP-117b. (arXiv:2006.05382v2 [astro-ph.EP] UPDATED)

Indications for very high metallicity and absence of methane for the eccentric exo-Saturn WASP-117b. (arXiv:2006.05382v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Carone_L/0/1/0/all/0/1">Ludmila Carone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Molliere_P/0/1/0/all/0/1">Paul Molli&#xe8;re</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhou_Y/0/1/0/all/0/1">Yifan Zhou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bouwman_J/0/1/0/all/0/1">Jeroen Bouwman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yan_F/0/1/0/all/0/1">Fei Yan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baeyens_R/0/1/0/all/0/1">Robin Baeyens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Apai_D/0/1/0/all/0/1">D&#xe1;niel Apai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Espinoza_N/0/1/0/all/0/1">Nestor Espinoza</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rackham_B/0/1/0/all/0/1">Benjamin V. Rackham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jordan_A/0/1/0/all/0/1">Andr&#xe9;s Jord&#xe1;n</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Angerhausen_D/0/1/0/all/0/1">Daniel Angerhausen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Decin_L/0/1/0/all/0/1">Leen Decin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lendl_M/0/1/0/all/0/1">Monika Lendl</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Venot_O/0/1/0/all/0/1">Olivia Venot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henning_T/0/1/0/all/0/1">Thomas Henning</a>

We investigate the atmospheric composition of the long period ($P_{rm orb}=$
10 days), eccentric exo-Saturn WASP-117b. WASP-117b could be in atmospheric
temperature and chemistry similar to WASP-107b. In mass and radius WASP-117b is
similar to WASP-39b, which allows a comparative study of these planets.

We analyze a near-infrared transmission spectrum of WASP-117b taken with
Hubble Space Telescope/WFC3 G141, which was reduced with two independent
pipelines. High resolution measurements were taken with VLT/ESPRESSO in the
optical. We report the robust ($3sigma$) detection of a water spectral
feature. Using a 1D atmosphere model with isothermal temperature, uniform cloud
deck and equilibrium chemistry, the Bayesian evidence of a retrieval analysis
of the transmission spectrum indicates a preference for a high atmospheric
metallicity ${rm [Fe/H]}=2.58^{+0.26}_{-0.37}$ and clear skies. The data are
also consistent with a lower-metallicity composition ${rm [Fe/H]}<1.75$ and a
cloud deck between $10^{-2.2} – 10^{-5.1}$ bar, but with weaker Bayesian
preference. We retrieve a low CH$_4$ abundance of $<10^{-4}$ volume fraction
within $1 sigma$ and $<2cdot 10^{-1}$ volume fraction within $3 sigma$. We
cannot constrain the equilibrium temperature between theoretically imposed
limits of 700 and 1000~K. Further observations are needed to confirm quenching
of CH$_4$ with $K_{zz}geq 10^8$~cm$^2$/s. We report indications of Na and K in
the VLT/ESPRESSO high resolution spectrum with substantial Bayesian evidence in
combination with HST data.

We investigate the atmospheric composition of the long period ($P_{rm orb}=$
10 days), eccentric exo-Saturn WASP-117b. WASP-117b could be in atmospheric
temperature and chemistry similar to WASP-107b. In mass and radius WASP-117b is
similar to WASP-39b, which allows a comparative study of these planets.

We analyze a near-infrared transmission spectrum of WASP-117b taken with
Hubble Space Telescope/WFC3 G141, which was reduced with two independent
pipelines. High resolution measurements were taken with VLT/ESPRESSO in the
optical. We report the robust ($3sigma$) detection of a water spectral
feature. Using a 1D atmosphere model with isothermal temperature, uniform cloud
deck and equilibrium chemistry, the Bayesian evidence of a retrieval analysis
of the transmission spectrum indicates a preference for a high atmospheric
metallicity ${rm [Fe/H]}=2.58^{+0.26}_{-0.37}$ and clear skies. The data are
also consistent with a lower-metallicity composition ${rm [Fe/H]}<1.75$ and a
cloud deck between $10^{-2.2} – 10^{-5.1}$ bar, but with weaker Bayesian
preference. We retrieve a low CH$_4$ abundance of $<10^{-4}$ volume fraction
within $1 sigma$ and $<2cdot 10^{-1}$ volume fraction within $3 sigma$. We
cannot constrain the equilibrium temperature between theoretically imposed
limits of 700 and 1000~K. Further observations are needed to confirm quenching
of CH$_4$ with $K_{zz}geq 10^8$~cm$^2$/s. We report indications of Na and K in
the VLT/ESPRESSO high resolution spectrum with substantial Bayesian evidence in
combination with HST data.

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